Unloadee eoe compeessoss and othee devices



F. D.. HOLDSWORTH AND C. w. wYMAN.

UNLOADER FOR COMPRESSORS AND OTHER DEVICES,

APPLICATION FILED DEC. 19| 1914.

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F. D. HOLDSWORT`H AND C. W. WYMAN. UNLOADER FOR COMPRESSOHS ANDOTHER DEVICES, APPLICATION' FILED nEc.19',1914.

1,404,175. Y Patented Jan. 17,1922.

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UNITED STATES FRED D. HOLDSWORTI-I AND CHARLES W. WYMAN, 01T CLAREMONT, NEW HAMPSHIRE,

rifles.

ASSIGNORS TO SULLIVAN' MACHNERY COMPANY, Ol?"CLREllrOl'l, NEW HAMP- SHIRE, A CORPORATION OF MASSACI-EUSETTS.

UNLOADER FOR COIVIPRESSORS AND OTHER DEVICES.

To (all `10.700772, t 77mg/ concern.'

Be it known that we, FRED D. HoneswoRTi-r and CHARLES W. WYMAN, citizens of the United States, and residents of Claremont, N. lil., have invented an Improvement in Unloaders for Compressors and other Devices, ot which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts. y

This invention relates to elastic Huid coniprcssors, and more'particularly to'con'ipressors ot the multi-stage type.

ln the operation of air compressors which are driven by an external source ot power which runs at a constant speed, such as electric motors, `gas or gasoline engines, in order to maintain a constant air pressure, it is necessary to interrupt the flow ot air through the machine when the pressure in the receiver reaches the desired point, and reestablish the flow as soon as the pressure .in the receiver has fallen a few pounds. rllhis is usually accomplished by placing a balanced valve, commonly called an unloading valve, on the main inlet supply to the compressor and attaching to this valve a suitable piston. which moves the valve to its open or'closed position under control ot a small regulator which is piped to the main air receiver. lVhen thisl unloading valve is closed as a result of the rise-in the receiver pressure, the compressor rapidly terms a more or less complete vacuum in all of its internal air passages. Owing to the construction ot this form of unloadingv valve, it is dillicult to make it absolutely airtight when it is closed', and it is dillicult to prevent other air leaks about the machine, so that a small quantity of air fiowsthrough the machine.y which air has to be compressed and dcliverml to the main receiver. lns'ead ot compressing this air trom ordinary atmospheric pressure however, it may be compressed vfrom only one or two pounds absolute pressure up to receiver pressure. This greatly increases the ratio o'liconision, and. as the heat generated in compression is directly dependent upon the Specification of Letters Patent. Patgutgd JguL 17, 1922. Application filed December 19, 1914. l

Serial No. 878,187.

number of times the air is compressed, it will readily be seen that when the air reaches it inal pressure in the air-cylinder, it will be heated very much in excess of the temperature obtained in compression under normal running conditions with the inletopening wide open. This high temperature is detrimental to the oil used for lubrication, and is a source of danger, inasmuch as the extreme heat may ignite the oil, or it the oil is diitused through the air in proper proportions, an explosion may result. This is especially true ot multi-stage compressors where the pressure is carried to several hundredpounds per square inch. This iuvention is more particularly concerned -with the provision of an auxiliary unloading valve which may be employed in connection with the second or high-pressure cylinder ot a two-stage compressor, or with the second and third `cylinders of; a three-stage compressor, or with the succeeding cylinders of a compressor of any desired number otl stages. this auxiliary valve there is a saving in power when running unloaded, as the small quantity of air flowing through the cylinder due to leakage is compressed 'and discharged at practically atmospheric pressure instead of receiver pressure. i

Our invention will be best understood by reference to the following description, when taken in connection with the accompanying illustration ot' one specific embodiment thereof, while its scope will be more or 'ticularly pointed out in the appended cl a ms.

ln the drawings:

l is a plan of a compressor embodying our invention;

Fig. 2 on an enlarged scale is a vertical section through an auxiliary unloading valve embodying the invention;

Figi'. 8 is a detail ot a modiiication to he referred to;

Fig. e is a longitudinal vertical section ot one end of a higrh pressure cyiin der which iu the present embodiment is ot the double acting' type, both ends being similar in construction; Y

Fig. 5 is an end elevation ot the low n u closed 1n Fig. 2.

Referring to the drawings and to thev embodiment of our invention which we have there disclosed, for illustrative purposes, we have there shown a multi-stage compressor, herein having two cylinders (Figz'l), a lowpressure cylinder 5 and a high pressure cylinder 6, Jthe former drawing its supply from an inlet pipe 7 (Fig. 5). The compressed a-ir is delivered by said low pressure cylinder to an intermediate receiver 11, which as is usual cools the air before it passes to the high-pressurel cylinder'. This receiver, which is commonly called an intercooler, delivers the air into an inlet chamber 12 (Fig. t) of the high-pressure cylinder 6,

whence it passes to an outlet chamber 13, as

will appear hereinafter. This outlet chamber in practice is connected toa main receiver which we have not shown herein as it is unnecessary to the illustration of our present invention.

Themain inlet 7 mayv be controlled as is usual by means of amain unloading valve 14 (Fig. 5) of the balanced type. This valve is usually controlled by a suitable piston which moves the valve to its open or closed position under control of a small regulator which is piped to the main air receiver, these parts being of usual and wellknown construction, and a further description of them being unnecessary to an understanding of our present invention.

Referring now to Fig. 4, there isV shown therein one end of the high pressure cylinder 6, herein of the double acting type, the other endA being precisely similar in construction. This cylinder is provided with a head 15 in which is located an inlet valve 16 which may be of any usual or desired construction, the same being herein of the oscillating type, being given an oscillating motion at the proper intervals in the operation of the machine by a suitableV mechanism (not shown).

The cylinder is also provided as usual with a discharge valve 17 which may be of any usual construction, herein being provided with a spring 18 tending to seat the same and operating as usual to open and permit the air compressed in the cylinder to flow into the outlet chamber 18 and thence to the usual main air receiver.

lVithin the cylinder 6 is a usual piston 19 which, when moved toward the right (Fig. et) draws the air through the inlet chamber 12 and its connections with the low pressure cylinder 5, and upon the closing of the inlet valve 16 the piston moves toward the left.

thereby compressing the air in the usual manner; and when the pressure in the cylinder is equal to or slightly greater' than the pressure in the discharge chamber 13 the discharge valve 17 will lift from its seat and allow the air to be forced out ofthe cylinder.

Next will be described the auxiliary unloading valve shown herein as applied to the high pressure cylinder. Since the latter is double acting an auxiliary valve is connected to each end of the cylindelgbut as the valves at both ends are similar a description of one willy suffice for both.

Referring more particularly to Fig. 2, this valve comprises a cylinder 20 mounted on a base 21 and communicating with chamber 21a therein, said base being connected by a pipe 22 with one end of the cylinder and by a pipe 23 with the outside atmosphere. This chamber has a wall 24 formed with a reverse bend presenting registering openings one of which is somewhat larger than the other and constituting seats for receiving a diiferential valve25 having a stem 27 guided* by a bore in a thickened portion of the lower wall of said base 21.

To' normally hold. said differential valve on its seatV there is provided in the cylinder 2O referred to a piston 28 urged downward by a heavy spring 29 confined between said piston and the top of said cylinder. To further contribute to the control of the differential valve, as more fully hereinafter described, it is pressed down on its seat by light helical spring 30- encircling a stud 31 projecting from av recessed hub 33 of said piston, said spring being confined between the end of the recess in said hub and the' differentiall valve. To further contribute to the guidance of the differential valve, its stem is extended upward into a bore 34 in saidy stud. A passage 35 completes the communication between the cylinder 20 and the pipe 22 and is provided with a spring pressed check valve 36. Y

In operation, after the unloading valve 14 is closedv by the rise in theV receiver pressure, the compressor rapidly forms a more or less complete vacuum in the cylinder 6. For example, when the compressor piston 19 moves toward the right (Fig. 4) it creates more or less of a vacuum in the cylinder on the left of the piston and also in the pipe 22, the chamber 21a and the passage 35. This opens the check valve 36 and creates more or less of a vacuum in the cylinder 20. The lower face of the piston 28 is continuously exposed to the outside atmosphere through the pipe 23. Consequently when a sullicient vacuum has been created in the cylinder 20, the piston 28 is lifted against the resistanceof the heavy spring 29 and the contact between said piston and the differential valve 25 is broken. As a result said valve becomes'free to lift against the pressure of thelight spring 30 and the pressure of the atmosphere.

When the compressor piston 19 returns to the Vleft of the cylinder, the small quantity of air in the cylinder at the leftof the piston under reduced pressure or partial vacuum will be compressed and, when the pressure thus formed slightly exceeds thepressure of the atmosphere, thefdifferential valve will rise from its'seatsV and allow this air to escape to the atmosphere -through the pipe28. f

After the receiver pressure has dropped slightly the'unloader valve 14 automatically opens in the usual manner and-the workv of compression is resumed. As the pressure builds uprin the inter-cooler and high, pressure cylinder, thel vacuum condition there is destroyed .and leakage `past the auxiliary valve piston 28 quickly destroysthe vacuum which existed above it. The piston is then forced downward by the heavy `spring 29 to and into engagement with the differential valvethereby holding itrfirmly to its seat. This springr is made sufficiently strong to hold the differential valve seated when the maximum working pressure of the compressor is obtained, so that none of the air compressedE in the normal operation of the compressor is wasted# Ifdesired, a minute vent hole 37 may be made in the cylinder 20 and be provided with afneedle valve 39 for regulating the opening therein. Thus the leakage of air into the cylinder 20 may be regulated Aand n controlled as required.

A singley disk valve might be employed in place of the differential valve shown herein, but if so a stronger spring would be required to hold 'the' valveto its seat and the piston and spring would not be as quickly responsive to the vacuum condition as those shown herein. It is therefore preferable to em'- ploy thev differential-valve.

As stated, auxiliary devicesare provided for both ends of the compressor cylinder. To insure simultaneous faction `in them'it is desirable to connect the cylinders 20 thereof by a small pipeV 41 (Fig. l). connected'the vacuum conditions in both of the chambers 20V above theirr pistons will be equalized andr said pistons will lift simultaneously out of contact with their differential valves and the air on the' opposite sides ofthe compressor'piston will be free to escape readily lpast the differential valves to the atmosphere. A

There are vvery important advantages in these auxiliary unloader valves, since after the pressure in the receiver has reached a predetermined'amount, they automatically release the air from the compressor and permit the latter to continue to operate Without performing any substantial work of compression. This llightens the burden onV the When thus driving mechanism for the compressor and prevents the objectionable high heating of the apparatus. It will be observed that these auxiliary unloader'valves are operated directly by the pressure condition within the compressor cylinder and independently of the pressure in the inter-cooler. By the direct connection of the auxiliary unloader valves to the cylinder it will also be noted that it is not only possible to utilize a higher vacuum and thus obtain greater certainty in operation of the valves, but it is also possible to eliminate entirely any connection between the valves and the intercooler. Attention is also directed to the fact that it is thus possible for the valves, if desired, to be applied to the usual indicator openings lfound in a standard compressor cylinder without any other change in the machine, the valve mechanism itself constituting a unitary device readily attachable toa standard machine. Also these auxiliary unloader valves do not operate simultaneously with the actuation of the main unloader valve, but subsequently thereto since the compressor piston must reciprocate to create a vacuum condition in the compressor cylinder suiiicient to lift the piston 28 against the resistance of the heavy spring back of it before the differential valve can open. Due to this retarded action, the partially compressed air in the intercooler is compressed to the receiver pressure instead of being discharged to the atmosphere. A further very important result obtained is that due to the fact that little air is left in the intercooler at the time that the unloading valve opens, the size of this valve may be very much smaller and still handle without undue resistance, the air rejected from the compressor during unloading' operation.

In Fig. 3 is shown a Inodiiication in which auxiliary unloading valves are provided substantially similar to the one described, but instead of being connected merely by a small pipe il (as shown in Fig. l), they are con*- nected by a pipe 43 having an intermediate branchpipe 45 connecting the same with the compressor cylinder near or at the middle of its lengthand provided with a check valve 47 therein. This check valve may be similar to the check valve l36 referred to and therefore it is not necessary to show the same in det-ail herein. This arrangement would render unnecessary the passage 35 and the locating of the check valve 36 therein.

In Fig. 2 the differential valve is shown as having guiding stems projecting in opposite directions therefrom. one being guided in a bore in the base of the casing and the other being guided in the hub ofthe spring pressed piston. In Fig. 6 is shown a modified construction comprising a differential valve 49 having a bore receivingr a guide stem or pin 5l made fast in a bore in the casing registering with the openings for the differential valve. lNhen the spring pressed piston is lifted from the valve the latter Will be free to slide on its stem When the pressure in the chamber exceeds the atmospheric pressure effect on the outer faces of said differential valve.

It will be observed that the lower hole for the differential valve and the hole for the guiding pin are of the samesize and may be made in one boring operation with the same tool, .thereby insuring the accurate alignment of the guide pin ivith the valve and the accurate fitting of said valve on its seats.

The differential valve with the bore therethrough as described finds a strong and substantialv guidance from the pin projecting upward therein. Since both ends of the differential valve are exposed to the outside atmospheric pressure, the bore in the valve may extend entirely therethrough Without any possibility of leakage into the chamber'.

lVhile ive have shown herein and described certain forms of the invention forl illustrative purposes and have disclosed and discussed in detail the construction and arrangement incidental to one specific appli'- cation thereof, it is to be understood that the invention is limited neither-to the mere details nor to the relative arrangement of parts nor to its specific embodiment herein shown, but that extensive deviations from the illustrated form of embodiment of the invention may be made and the unloader valve claimed herein may be applied to a variety of other uses all without departing from the principles of the invention.

That We claim and desire. to secure by Letters Patent is: Y

l. The combination of an air compressor cylinder and its piston with a main unloader valve therefor, an auxiliary unloader valve, and means responsive to avacuum condition in said cylinder 'proper for openingsaid auxiliary unloader valve to relieve the work on said piston.

2. The combination of an air compressor cylinder and its 'piston with a main unloader valve therefor, and valve means responsive to a vacuum condition in one end of said cylinder proper for automatically relieving the Work on said piston a substantial length of time after the closing of said main unloader valve.

3. The combination of an air compressor cylinder and its piston with unloader valve means for automaticallyr shutting off the inlet supply of air to said cylinder, and valve means directly responsive to a vacuum condition in'one end of said cylinder proper operating after the closing of said unloader valve means to relieve the compressing Work of said piston.

4. The combination of an air compressor cylinder and its piston with means for auto- Vtial valve.

matically shutting off. thefinl'et supply of air thereto, and valve mechanisms for relieving the ivorlr on said piston on the production of .a vacuum condition in said Ycylinder by said piston.v

5. The combination of; an air compressor cylinder and its piston, with means for automatically shutting-offvthe' inlet supply of air thereto, and simultaneously acting valve mechanisms at each endv of'said cylinder directly responsive to.' cylinder pressure for reducing the Work done in said cylinder by said piston. I

r6. The combination of an air compressor cylinder and its piston, With an unloader mechanismfV therefor comprising; a valve, means normally closing said valve, and means responsive tol a vacuum condition in said compressor cylinder' for releasing said closing means. Y f

7. The combination'of an aircompressor cylinder and `its piston with an unloader valve therefor, comprisinga valve, a spring pressed piston lfor normally closing said valve, av cylinder'for the'latter piston, and mea-ns providing communication between said cylinders for permittingl the creating byy said compressor piston. of avacuum condition back of :said spring pressed. piston.

8. A compressor controllingvalve mechanismcomprisinga casingcontaining a chamber having a Wall formed to present registering valve seats, a differential valve, a spring pressed piston for normallyholding Vsaid valve on its seats, anda cylinder for said piston, said valve beingY operated in one direction bythe pressure on the differen- 9. A compressor controlling valve mechanism comprisingy a casing having a Wall formed to present valve seats, a differential valve, aspring pressed piston for normally holding said valve on Yits seats, and a cylinder for said piston, said-valve being operated iny one direction bythe pressure oni the differential' valve.

l0. A compression controlling valve mechanismcomprising a casing having a chamber therein, Ya differential valve for said chamber, a spring pressed' piston .for normally closing said valve, and a cylinder for said piston', said valve being operated in one direction bythe pressure on the .differential valve.

l1. A compressor controlling valve mechanism comprising. Va casing containing a chamber having a wall formed to present registering valveV seats, a differential valve, a. spring pressed piston for normally holding said valve on its seats, aV cylinder for said piston, and means for actuating said piston to release said valve.

l2. A compressor controlling valve mechnism comprising a casing having a Wall formed to present valve-seats, a differential valve, a spring pressed piston for normally holding said valve on its seats, a cylinder tor said piston, and means for unbalancing said piston to release said valve.

lf3. A compressor controlling valve mechanism comprising a casing having a chamber therein, a differential valve for said chamber. a spring pressed piston for normally closing said valve, a cylinder for said piston, and means for subjecting the different cnds of said piston to different pressures.

111-. compression controlling valve mechanism comprising a casing, a chamber therein.I valve means for controlling communication of said chamber with the atmosphere, a spring pressed piston for normally closing said valve, one side of said piston being exposed to the atmosphere, and means for creating a vacuum condition on the opposite side of said piston to release the same from said valve.

15, A compressor controlling valve mechanism comprising a casing containing a chamber, a valve for controlling communication of said chamber with the atmosphere, piston means for normally closing said valve, and means for unbalancing the pressure on said piston to release the latter from said valve.

1G. A compressor controlling valve mechanism comprising a casing having a chamber therein, a valve for controlling the communication ot said chamber with the atmosphere, means acting on said valve to normally close the latter, andmeans for unbalancing the same to release said valve.

17. A compressor controlling valve mechanism comprising a casing containing a chamber, a valve for controlling the communication of said chamber with the atmosphere, spring pressed means acting on said valve normally to close the same, and means for unbalancing the pressure on said spring pressed means to release the same from said valve.

1S. The combination of an air compressor cylinder and its piston with an unloader valve mechanism therefor comprising a valve. a cylinder.` a piston in said cylinder, a spring acting ou said valve to hold the latter normally closed, said spring being suihciently strongl to hold said -valve closed when the compressor develops a predetermined pressure, a main unloader valve for cutting off the inlet supply of air to the compressor' cylinder, and means cooperating with the compressor piston and adapted to create a vacuum condition in said valve piston cylinder.

19. A. compressor controlling valve mechanism comprising a casing containing a chamber, a valve for said chamber, a cylinder, and a spring pressed piston in said cylinder for normally closing said valve, said cylinder having a minute passage Ol permittingthe leakage of atmospheric pressure therein.

20. A compressor controlling valve mechanism comprising a casing containing a chamber, a valve for said chamber, a cylinder, a spring pressed piston in said cylinderl ttor normally closing said valve, and needle valvel means for permitting the leakage of atmospheric pressure into said cylinder.

f Zl. A compressor cont-rolling valve mechamsm comprising a cylinder containing a chamber having a wall formed to present registering valve seats, a valve having dif- Jferential elements adapted to set on said seats, and a guiding stem for said valve, said valve being operated in one direction by the pressure on the differential elements.

22. The combination ot a casing contain.- ing a cylinder and a chamber and having an opening communicating with the outside atmosphere, a wall in said casing formed to present a valve seat, a valve cooperating with said seat, a piston in said cylinder having a face exposed to the outside atmosphere, a spring in said cylinder for pressing said piston toward said valve to hold the latter normally seated, means for creating a vacuum in said cylinder, and a check valve for said cylinder.

23. The combination of an air compressor cylinder' and its piston with unloader valve mechanisms connected with opposite ends of said cylinder, each comprising a valve, a spring pressed piston for normally closing said valve, a cylinder containing said piston, said piston being adapted upon a drop of pressure in the cylinder, to permit the valve to open, and means connecting the spring pressed piston containing cylinders of the two mechanisms t'or equalizing the vacuum conditions therein.

24. The combination of an air compressor cylinder and its piston with valve mechanisms for the opposite ends of said cylinder, each comprising a valve, a spring pressed piston for normally closingsaid valve, a cylinder for said piston, a pipe connecting the spring pressed piston containing cylinders oi the two mechanisms,'and a pipe connecting` said pipe with said air compressor cylinder.

25. The combination of an air compressor cylinder and its pist-on with unloader valve mechanisms for the opposite ends ot s aid cylinder, each comprising a. valve, a spring pressed piston for normally closing said valve and a cylinder containing the same; and means providing communication between said valve mechanism cylinders and with said air compressor cylinder.

26. The combination of an-air compressor cylinder and its piston with unloader valve mechanisms for the opposite ends of s aid cylinder, each comprising a valve, a spring Pressed Pistonv ter sense/11i @here Seid leasing' said piston from said valve to per-V mit the opening;l thereof' against the resistance ot said First mentioned spring` 2S. The combination ot an air compressor Cylinder and its piston, With an auxiliary unloader valve mechanism therefor comprising` a valve, a spring tendinsor to elose said valve, a spring pressed piston 'for normally Closing said *valve`r and means responsive to pressure Conditions in said Compressor eylinder for releasing` said piston from said valve to permit the opening: thereof the resistance of said iirst mentioned spring.

29. The Combination of an air compressor cylinder and its piston with a main unloader valvev and an auxiliary unloadingl valve mechanism comprising a valveI` a light spring tending to Close the same1 a pisto heavy spring acting on said piston :tor normally holding said valve seated, and means for unbalaeingY the pressure on said sprinr pressed piston to release the ame from said valve.

30. rEhe Combination of an air compressor Cylinder and its piston, with a main unloader valve and an auxiliary unloading' valve mechanism Comprising' valve. a light spring tending` to Close the same, a piston, a heavy spring acting on said piston for normally holding said valve seated,y and means responsive to vacuum conditions in said linder for unbalaneing the pressure on id spi-iin;` pressed piston to release the same from said valve,

3l. r he romhimltion oit an air compressor Cylinder and its piston with a main unloader valve therefor, an auxiliarj.' unloader valve, means for normally elosiugr thelatter valve7 and n'ieans responsive to the pressure condition in said cylinder proper for releasinn' said Closing means Yfrom said auxiliary valve.

3L. The combination ollv an air compressor cylinder-and its piston with a main unloader valve, a relief valve1 a pressure responsive means for normally holding said relief valve closed and having provision for releasing said valve on the occurrence of a predetermined drop in pressure in said cylinder. Y

The Combination oiE an air compressor cylinder and its piston with a main unloader valve therefor for automatically shutting olf the inlet supply of air to said cylinder and an auxiliary unloader valve, means 'for normally holding said auxiliary valve closed, and means responsive to a drop in pressure in said elyinder proper for releasing said valve holding means.

ill, 'lf he Combination or an air compressor cylinder and its piston 'with a relief valve therefor; and ilnessure responsive mea-ns ior normally holding said valve Closed and having` )revision responsive to a drop in pressure in said Cylinder proper for permitting said relief valve to open.

55. 'he Combination ot an air compressor cylinder and its vilriiston with a relie'f zelve, pressure responsive means normally holding,` said valve closed7 and means providing eonnnunieation between said pressure responsive means and said Cylinder for automatically releasing said pressure means Atrom said valve on the occurrence of a predetermined drop in pressure in said cylinder.

36. The Combination el' an air Compressor Cylinder and its pistonY with a relier" valve therefor, pressure responsive means for normally holding said valve closed, passage means connecting; said pressure responsive means and` cylinder, and eheelr Valve means for said passage means.

317. The combination of an air Compressor Cylinder audits piston with a relier' valve therefor, pressure responsive means for normally holding` said valve seated, passage means Connecting said pressure responsive means with said cylinder and having,` provision permitting the release of said pressure responsive means from said valve on Vthe oeeurrenee of a predetermined drop in pressure in said Cylinder, and means for automatically permitting the reseating of said valve hy said pressure responsive means 3S. The combination oi an air Compressor cylinder and its piston With a relief Valve therefor, pressure responsive means for normally holding said valve closed, passage means connecting said pressure responsive means with said cylinder and having provision permitting the 'release oi' said pressure responsive means from said valve on the weurrenee of a predetermined drop in pressure in said cylinder` and means vermitting the leakage of atmospherie pressure to said pressure responsive means to render the latter elleetive to hold said valve in closed position. y

39. The Combination of a compressor cylinder and its pistoman unloader valve oommunieatingwith the cylinder and the atmospherel` means for normally holding said val Ve Volosed, controlling means for said closingi means eonneeted lto said cylinder, and means Yfor controlling' said connection.

L10. The eomhination of compressor Cylinder and its pistoni; an unloader valve oom- 'munieating with the Cylinder and the atmosphere, means for normally holding saidV valve closed, Controlling means for said closing means connected to said cylinder, and intermittently operating valve mechanism controlled by said piston for controlling said connection.

4l. The combination of a compressor cylinder and its piston, a main unloader valve, an auxiliary unloader valve communieating with the cylinder and the atmosphere, means' for normally holding saidfauxiliary valve closed, controlling means for said closing means ,connected to said cylinder proper, and means operative after the closure of said main unloadervalve for controlling rsaid connection.

42. The combination :of a comp-ressor cylinder and its piston, a main unloader valve, an auxiliary unloader valve communicating with the cylinder andthe atmosphere, means for normally holdingsaid auxiliary valve closed, controlling means for said closing means connected to said cylinder, and intermittently operating valve mechanism controlled by said piston controlling said connection.

43. The combination of a compressor cylinder and .its piston, a main unloader valve, an auxiliary unloader valve communicati ng with the cylinder and the atmosphere, means for normally holding said auxiliary valve closed, controlling means for said closing means connected to said cylinder, and means operative after the closure of said main unloader valve .for closing the connection between said cylinder and said controlling mechanism during the compression stroke of the piston and opening said connection during the suction stroke thereof.

44. The combination of an air compressor cylinder and its piston with a main unloader valve therefor, an auxiliary unloader valve, and mea-ns responsive to pressure changes in said cylinder proper or open ing' said auxiliary unloader valve to relieve the work on said piston.

45. The combination of an air compressor cylinder and its piston with a main unloader valve therefor, an auxiliary unloader valve, and means havingr communication with the'opposite ends of said cylinder and responsive to pressure changes in said cylinder propel' for openingr said auxiliary unloader valve to relieve the work on said piston.

46. In combination with an air compressor having a cylinder and piston therein, a main unloading valve, an auxiliary unloadingr valve, means normally closing said auxiliary valve, and a direct connection between said means and said cylinder whereby the pressure variation produced by a stroke of the compressor piston in one direction releases the unloading valve for operation by the pressure variation produced on the return stroke;

47. In combination with an air compressor having a cylinder and a main unloading valve, an auxiliary unloading' valve tor each end of the cylinder, means for normally holding' said auxiliary valves seated, andV a' direct connection between said means and said cylinder,r proper whereby a reduced pressure produced at one end of said cylinder may `release the unloading valve at the opposite end ot said cylinder.

In combination with an air comprersor 'having a cylinder and a main unloading valve, an auxiliary unloading valve for each end'of the cylinder, means for 'normally' holding' said auxiliary valves seated, and a direct connection between said means and said cylinder proper whereby a reduced pressure produced at one end off said cylinder may release the unloading-valve at the same end 'of said cylinder.

49. In combination with an air compressor having a cylinder, automatic relief valve means for unloading the compressor having a connection with the atmosphere, means for normally maintaining said relief valve means closed, and means for effecting opening; thereof, said means including a member having opposed surfaces one of which is exposed to the atmosphere and the other oli which is connected with the cylinder, and means for permitting` the How of fluid in one direction only between said last mentioned surface and the cylinder, said reliet valve means including a member controlling" the said atmospheric connection and having a. surface having; a continuously open connection with the cylinder permitting flow to or from said surface.

50. In `an unloading' means for a double acting compressori` cylinder, means torirninga pair of passages adapted to communicate with the end's of a cylinder7 a pair of valves controlling the communication of said passages with the atmosphere, means normally operatingT to hold said valves closed, and controlling means for said holding means connected with said passages.

51. In an unloading means for a double actingr compressor cylinder. means forming a pair of passages adapted to communicate with the ends of a cylinder, a pair of valves controlling the communication of said passages with the atmosphere, and means normally operating,r to hold said valves closed, the holding means for one of said valves being connected with the passage controlled by the other valve.

52. In an unloading; means for a double acting compressor cylinder, means forming a pair of passages adapted to communicate with the ends of a cylinder, a pair of valves controlling the communication of said pa sage with the atmosphere, means normally operating to hold said valves closed, and means wheneby said holding `means may be subjected to pressure variations in the opposite ends of a cylinder.

In combination with a double acting compressor cylinder having a main yunloader valve adapted to-close the intake of the cylinder, a supplemental unloading valve oomprising passages communicating with said cylinder at point-s relatively longitudinally distant fromy yeach other, valves adapted when operated to permit communication be.- tween said passages and the atmosphere-7 means to hold said valves normally closed, and means adapted to oonneetsaid last mentioned means .With the passages at the opposite ends of the Cylinder therefrom Where-l by a reduced pressure in one end of said cylinder may be transmitted to the opposite holding means. Y

pherie on said second mentioned surface and having a direct communication with an end of vthe cylinder.

In testimony whereof WeV have signed our names to this specification in the presence of two subscribing witnesses.

FRED D. HOLDSWORTH. CHARLES W. WYMAN.

Vitnesses:

E. A.. TRACY, M. A. HENRI. 

